linux-kernel - detecting integer constant expressions in macros

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Message-ID: <1521584015.31174.3.camel@med.uni-goettingen.de>
Date:   Tue, 20 Mar 2018 22:13:35 +0000
From:   "Uecker, Martin" <Martin.Uecker@....uni-goettingen.de>
To:     "torvalds@...ux-foundation.org" <torvalds@...ux-foundation.org>
CC:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: detecting integer constant expressions in macros


Hi Linus,

here is an idea:

a test for integer constant expressions which returns an
integer constant expression itself which should be suitable
for passing to __builtin_choose_expr might be:

#define ICE_P(x) (sizeof(int) == sizeof(*(1 ? ((void*)((x) * 0l)) :
(int*)1)))

This also does not evaluate x itself on gcc although this is
not guaranteed by the standard. (And I haven't tried any older
gcc.)

Best,
Martin